This invention relates to a method for producing an electrolyte, comprising, at least one first polymer, called the complexing polymer, having at least one hetero atom in its monomer pattern, together with at least one complexed ionizable alkaline salt in the said polymer.
A number of studies have been conducted on such electrolytes.
French Pat. No. 2 442 513 presents an electrolyte of this type in which the polymer carries, partially or totally, the homo and/or copolymers, essentially noncross-linked chains, derived from one or several monomers holding a heteroatom capable of forming donor-acceptor type links with the ionizable salt cation.
However, the complex formed has a strong tendency to crystallize at ambient temperature (reduction of the lability between chains), a temperature which is below the melting temperature of the crystallites, which considerably reduces ionic mobility within the network.
The consequence of such a property is a substantial reduction in the ionic conductivity between 100.degree. C. and ambient temperature, a reduction which makes it necessary to use such solid polymer electrolytes above 80.degree. C., because it is necessary to reach the melting temperature of the crystalline zones to obtain enough ionic conductivity, e.g. about 10.sup.-4 (ohm.cm).sup.-1.
Also known, i.e. from European patent application No. 0 037 776, is the use of polymers or oligomers, which are cross-linked, in particular chemically, to constitute the complexing polymer, with as low a vitreous temperature as possible.
However, such polymers have proved to have little use as solid electrolytes in electrochemical cells in ambient temperature applications because of their ionic conductivity and because of the instability of the cross-links in the presence of the electrodes, in particular the negative electrode; this is particularly the case for di, tri or multi isocyanate chemical cross-linking in relation to lithium, which reduces them.
The embodiments of the present invention solve the above problems.